The present invention relates to a multiple speed induction motor and particularly to an induction motor having a running winding means and a starting winding means which is disconnected as the motor reaches or approaches operating speed.
The induction motor is widely employed in industrial, institutional and domestic applications. Single speed induction motors are constructed with a run winding connected in parallel with a starting winding and a series connected phase shift capacitor. A centrifugal switch unit or an electromagnetic switch unit is connected in the circuit of the start winding to disconnect the start winding at a selected speed. Although centrifugal and mechanical switches have been employed for many years, solid state switches devices have more recently been provided in place of the centrifugal switch. For example, General Electric application note 200.35, page 16, discloses an AC split-capacitor start motor in which a starting winding is connected in parallel with the running winding. The starting winding circuit includes a starting capacitor and a solid state switch shown as a "Triac". The solid state switch has a gate circuit coupled to the incoming power supply lines through a current transformer. The solid state switch is gated on only until the motor approaches running speed and then turns off to disconnect the start winding with the motor current at the normal operating level. The solid state switch replaces the conventional centrifugal switch or electromechanical relay. In either instance, the cut out switch is designed to open at a selected speed thereby removing the starting winding and maintaining motor operation under efficient operating conditions with only the running winding connected to the power lines. In certain applications, different but constant speeds may be desired. Multiple speed induction motors have been suggested in which the connection of a winding means which is wound in different pole arrangements is selectively connected in circuit by a selection switch and a centrifugal switch to permit operation of the motor at different speeds and with a single start winding unit. For example, U.S. Pat. No. 26,179 to Brammerlo et al which issued Mar. 21, 1967 discloses a multiple speed induction motor having a first run winding which is wound as a four pole winding and a second combined start and run winding which is wound as a six-pole winding. A centrifugal switch connects the six-pole winding in circuit as a start winding and the four-pole winding as the run winding, such that the motor always starts as a four-pole motor. The motor however runs as either a four-pole motor or a six-pole motor depending upon the positioning of a mechanical selection switch which connects the incoming power supply lines to the windings in different arrangements. For four-pole motor operations, the centrifugal switch disconnects the second start winding and leaves only the first winding in circuit. For six-pole motor operation, the second start winding is reconnected to operate as a six-pole run winding with the first winding disconnected. Other patents which similrly show means for switching between four-pole operation and six-pole operation include U.S. Pat. No. 2,774,024 and 1,918,323.
Although such dual speed motors have been suggested, there is a need for a simple but reliable winding and switch control for such a dual wound and speed motor.